Traveling wave maser amplifiers typically utilize a reverse isolation structure to attenuate microwaves traveling opposite to the forward direction along which signals are intended to be amplified. One type of isolator structure includes a continuous strip of constant cross section formed of garnet or ferrite material such as yttrium iron garnet (YIG) that extends along most of the length of the amplifier slow-wave structure. While such a continuous strip is relatively easy to fabricate and mount, it is fairly lossy, so there is perhaps an 8 to 10 db loss of signal traveling in the forward direction caused by the isolator. An important contributor to losses in such a continuous strip, is the presence of isolator material in the areas of the amplifier that are not circularly polarized.
Another type of isolator structure includes individual elements of YIG spaced at intervals along the length of the amplifier slow-wave structure, so that the isolator elements lie primarily in the circularly polarized regions of the amplifier. Such an isolator produces smaller losses. However, the isolator elements must be extremely thin, and involve greater efforts in fabrication and in accurately mounting them in place than for a continuous strip. For example, in mounting YIG elements for an X-band maser, where each element had a thickness of about 0.002 inch and where the thickness of each element was controlled to 0.00005 inch tolerance, it was found that the elements were extremely fragile and difficult to fabricate. An isolator structure which was somewhat easier to fabricate, and which produced low loss over a wide bandwidth, would be of considerable value.